Photoluminescence and cathodoluminescence measurements on a variety of GaN samples confirmed earlier reports that epitaxial lateral over-growth resulted in improved material quality. Depth profiling of epitaxial lateral over-growth samples, reported here for the first time using variable energy electron beam excitation, showed that there was a substantial reduction in defect density away from the interface, and that the barriers to defect propagation were very effective. In addition to the normal yellow emission generally observed for GaN, intense blue emission was found, already attributed to a metastable defect, in some materials. Using a rapid scanning interferometer, a study was made of changes in the luminescence spectrum as a function of time and at a range of temperatures. Possible explanations were suggested for the complex nature of the metastability displayed by the defect responsible for the blue band.

Evaluation of the Optical Properties of Epitaxial Lateral Overgrown Gallium Nitride on Sapphire and the Role of Optically Active Metastable Defects using Cathodoluminescence and Photoluminescence Spectroscopy. B.J.Ryan, D.P.Lowney, M.O.Henry, P.J.McNally, E.McGlynn, K.Jacobs, L.Considine: Thin Solid Films, 2005, 473[2], 308-14